Former MP Ann Widdecombe is reportedly being lined up as the next British ambassador to the Vatican. Photograph: David Levenson/Getty Images

If Ann Widdecombe is really a serious candidate as the next British ambassador to the Vatican, should we next expect the appointment of Melanie Phillips as ambassador to Washington? They are not as different as they may seem – both of them intelligent and energetic women, wildly out of step with majority British beliefs on the things they really care about, and neither known ever to express someone else's opinion. These are qualities that make for good columnists, but the role of a diplomat is a little different.

The British ambassador to the Holy See is someone whose job is to understand and mutually interpret the attitudes of the Vatican and the British government and to broaden their mutual sympathy. I can't easily imagine Widdecombe expressing anyone else's opinions, yet that is one of the central skills of diplomacy.

Purely as a piece of symbolism, there is something in this appointment to upset most people. For the Vatican, there is the fact of a woman who won't hesitate to tell them what to do; but she won't, when she does so, be representing any significant strand of British opinion. Since she left the Church of England in principled disagreement over women priests, she clearly represents a minority opinion among British Christians. Her contempt for Anglicanism doesn't really fit her to explain the religious landscape of this country. For secularists she is anyway anathema, rather like the post she is proposed to fill.

Within the Catholic church, as a prominent straight single lay conservative, she forms part of a minority of, oh, about two. She is certainly not the candidate of the Bishops' conference, but she has also been attacked by the conservative Damian Thompson, who calls her the rudest woman in Britain, and the liberal circles around the Tablet think she would be a catastrophe.

This is not an appointment that could be made by anyone who thought Britain's relationship with the Vatican was something that really mattered. After all, Melanie Phillips is not going to be our ambassador in Washington.

Now it may well be that the whole thing is a joke, a rumour got up to please her. She must fancy the job or she would have denied the stories more vehemently than has happened. The superficial advantage for the British government of having her as ambassador in Rome is that she would be in Rome, and not underemployed in the House of Lords. But no one in the House of Lords can make very much trouble, whereas diplomats who can't manage diplomacy can damage their country's interests.

There is only one decent argument for her appointment: even though she's an amateur, she can't be less diplomatic than the supposed professionals who produced the memo suggesting that the Pope endorse a brand of condoms when they were asked to plan for his visit. Nor is she likely to run off with a journalist or even a gogo dancer as recent ambassadors elsewhere have done. But if we are to have an ambassador to the Vatican at all, we should have one who knows something about diplomacy, and not just foreign policy.